Method for controlled application of reactive vapors to produce thin films and coatings

ABSTRACT

A vapor phase deposition method and apparatus for the application of thin layers and coatings on substrates. The method and apparatus are useful in the fabrication of electronic devices, micro-electromechanical systems (MEMS), Bio-MEMS devices, micro and nano imprinting lithography, and microfluidic devices. The apparatus used to carry out the method provides for the addition of a precise amount of each of the reactants to be consumed in a single reaction step of the coating formation process. The apparatus provides for precise addition of quantities of different combinations of reactants during a single step or when there are a number of different individual steps in the coating formation process. The precise addition of each of the reactants in vapor form is metered into a predetermined set volume at a specified temperature to a specified pressure, to provide a highly accurate amount of reactant.

This application is related to Provisional Application Ser. No.60/482,861, filed Jun. 27, 2003 and entitled: “Method And Apparatus forMono-Layer Coatings”; Provisional Application Ser. No. 60/506,846, filedSep. 30, 2003, and entitled: ““Method Of Thin Film Deposition”; and,Provisional Application Ser. No. 60/482,861, filed Oct. 9, 2003, andentitled: “Method of Controlling Monolayer Film Properties”.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to apparatus and a method useful in thedeposition of a coating on a substrate, where the coating is formed fromchemically reactive species present in a vapor which is reacted with thesubstrate surface.

2. Brief Description of the Background Art

Both integrated circuit (IC) device fabrication andmicro-electromechanical systems (MEMS) fabrication make use of layers orcoatings of material which are deposited on a substrate for variouspurposes. In some instances, the layers are deposited on a substrate andthen are subsequently removed, such as when the layer is used as apatterned masking material and then is subsequently removed after thepattern is transferred to an underlying layer. In other instances, thelayers are deposited to perform a function in a device or system andremain as part of the fabricated device. There are numerous methods fordepositing a thin film layer or a coating, such as: Sputter deposition,where a plasma is used to sputter atoms from a target material (commonlya metal), and the sputtered atoms deposit on the substrate. Chemicalvapor deposition, where activated (e.g. by means of plasma, radiation,or temperature, or a combination thereof) species react either in avapor phase (with subsequent deposition of the reacted product on thesubstrate) or react on the substrate surface to produce a reactedproduct on the substrate. Evaporative deposition, where evaporatedmaterial condenses on a substrate to form a layer. And, spin-on,spray-on, or dip-on deposition, typically from a solvent solution of thecoating material, where the solvent is subsequently evaporated to leavethe coating material on the substrate.

In applications where the wear on the coating is likely to occur due tomechanical contact or fluid flow over the substrate surface on which thelayer of coating is present, it is helpful to have the coatingchemically bonded directly to the substrate surface via reaction of thespecies with the surface in order to obtain particular surfaceproperties.

With respect to layers and coatings which are chemically bonded to thesubstrate surface, areas of particular current interest are those ofintegrated circuitry, and a combination of integrated circuitry withmechanical systems, which are referred to as micro-electromechanicalsystems, or MEMS. Due to the nanometer size scale of some of theelectrical devices formed, and the use of MEMS in applications such asthe biological sciences, where the type and properties of the coating onthe substrate surface is used to provide a particular functionality tothe surface, a need has grown for improved methods of controlling theformation of the coating or layer on the substrate surface.Historically, these types of coatings were deposited in the liquidphase, resulting in limited film property control and loss of deviceyield due to capillary forces. More recently, vapor-phase deposition hasbeen used as a way to replace liquid processing and to improve coatingproperties.

For purposes of illustrating a few of the many potential applicationsfor vapor phase coatings, which must either be deposited to haveparticular critical properties and/or to have particular permanentstructural orientation relative to the underlying substrate, applicantswould like to mention the following publications and patents whichrelate to methods of coating formation. Applicants would like to make itclear that some of this Background Art is not prior art to the presentinvention because it has been published at such a time that it issubsequent to the date of invention for applicants' invention. It ismentioned here because it is of interest to the general subject matter.

Product applications employing coatings deposited on a substrate surfacefrom a vapor include the following, as examples and not by way oflimitation. U.S. Pat. No. 5,576,247 to Yano et al., issued Nov. 19,1996, entitled: “Thin layer forming method where hydrophobic molecularlayers preventing a BPSG layer from absorbing moisture”. U.S. Pat. No.5,602,671 of Hornbeck, issued Feb. 11, 1997, which describes low surfaceenergy passivation layers for use in micromechanical devices. Inparticular, an oriented monolayer is used to limit the Van der Waalsforces between two elements, reducing the attraction between thesurfaces of the elements. An article by Steven A. Henck in TribologyLetters 3 (1997) 239-247, entitled “Lubrication of digital micromirrordevices”, describes nearly fifty lubricants which were investigated foruse in a digital micromirror device. The lubricants includedself-assembled monolayers (SAMs), fluids, and solid lubricants. Thelubricants were used to reduce the adhesion between contacting surfaceswithin a microelectromechanical system (MEMS) device. In an articleentitled “Vapor phase deposition of uniform and ultrathin silanes”, byYuchun Wang et al., SPIE Vol. 3258-0277-786X(98) 20-28, the authorsdescribe uniform, conformal, and ultrathin coatings needed on thesurface of biomedical microdevices such as microfabricated siliconfilters, in order to regulate hydrophilicity and minimize unspecificprotein adsorption. Jian Wang et al., in an article published in ThinSolid Films 327-329 (1998) 591-594, entitled: “Gold nanoparticulate filmbound to silicon surface with self-assembled monolayers, discuss amethod for attaching gold nanoparticles to silicon surfaces with a SAMused for surface preparation”.

Patrick W. Hoffman et al., in an article published by the AmericanChemical Society, Langmuir 1997, 13, 1877-1880, describe the molecularorientation in monomolecular thin organic films and surface coverage onGe/Si oxide. A gas phase reactor was said to have been used to provideprecise control of surface hydration and reaction temperatures duringthe deposition of monofunctional perfluorated alkylsilanes. Althoughsome process conditions are provided, there is no description of theapparatus which was used to apply the thin films. T. M. Mayer et al.describe a “Chemical vapor deposition of fluoroalkylsilane monolayerfilms for adhesion control in microelectromechanical systems” in J. Vac.Sci. Technol. B 18(5), Sep/October 2000. This article mentions the useof a remotely generated microwave plasma for cleaning a silicon oxidesubstrate surface prior to film deposition, where the plasma source gasis either water vapor or oxygen. U.S. Pat. No. 6,203,505 to Jalisi etal., issued Mar. 20, 2001 describes guide wires having a vapor depositedprimer coating. The guide wires are an intraluminal device having anadhesive primer coat formed of a carbonaceous material and a lubricioustop coat of a hydrophilic polymeric material. One preferred coatingmethod for applying a carbon-based primer coating is chemical vapordeposition. The coating is a plasma polymerized coating, so that theresulting polymer is an amorphous structure having groups in thestructure other than the monomer groups of the source materials. Forexample, plasma polymerized polyethylene may include a variety offunctional groups, such a vinyl, in addition to the methylene groups. Intheir article entitled: “Amino-terminated self-assembled monolayer on aSIO2 surface formed by chemical vapor deposition”, J. Vac. Sci. Technol.A 19(4), Jul/August 2001, Atsushi Hozumi et al. describe the formationof self-assembled monolayers (SAMs) on n-type Si (100) wafers which werephotochemically cleaned by a UV/ozone treatment, whereby a thin SiO₂layer was formed on the silicon surface. The SAM coating was applied byplacing a cleaned wafer together with a silane liquid precursor dilutedwith absolute toluene into a container having a dry nitrogen ambientatmosphere. The container was sealed with a cap and heated in an ovenmaintained at 373°K.

International Patent Application No. PCT/US01/26691, published on Apr.11, 2002, describes substrates having a hydrophobic surface coatingcomprised of the reaction products of a chlorosilyl group compound andan alkylsilane. In a preferred embodiment, a hydrophobic coating isformed by the simultaneous aqueous vapor phase deposition of achloroalkylsilane and a chlorosilyl group containing compound to form ananchor layer, which may then be capped with a hydrophobic coating. Thereactants are said to be vapor-deposited simultaneously in a closedhumidity-controlled chamber. Dry air, humid air, or dry air saturatedwith coating precursor vapor was introduced at one end of the chamberand exhausted at the other. The reaction precursors are said to beintroduced into the reaction chamber by flowing dry air over theprecursor liquid and into the chamber. U.S. Pat. No. 6,383,642 to LeBellac et al., issued May 7, 2002 described formation of ahydrophobic/oleophobic coating on a substrate such as a glass or plasticmaterial. The coating precursor is introduced into a chamber whichemploys a pulsed plasma, with the frequency of the plasma generationsource ranging from 10 kHz to 10 GHz at a power from 100 to 2000 W,where the substrate surface area to be coated is 0.4 M². The precursorsare introduced into the chamber at various flow rates to establish andmaintain a pressure in the chamber ranging from 0.1 to 70 Pa.

W. Robert Ashurst et al., discuss a method of applying anti-stictioncoatings for MEMS from a vapor phase in an article published by ElsevierScience B. V., in Sensors and Actuators A 104 (2003) 213-221. Inparticular, silicon (100) samples cut from a P-doped, n-type test waferare rinsed in acetone and then cleaned by exposure to UV light and ozonefor 15 minutes. The samples are treated with concentrated HF for 10minutes and then cleaned again as described above before introduction toa vapor deposition chamber. In the vapor deposition chamber, the siliconsubstrates are additionally cleaned of any organic contamination usingan oxygen plasma which is generated in the coating chamber, but at asufficient distance away from the samples that the samples can becontacted by plasma species without being inside the plasma dischargearea. After O₂ plasma exposure was begun, water gas was dosed into thechamber and eventually displaced the oxygen. The water was added to form—OH surface terminations oil the substrate surface. The coating wasapplied by first admitting water vapor to the chamber until the pressurein the chamber exceeded 5 Torr. Subsequently, the chamber was evacuateddown to the desired water vapor pressure between 1 and 1.3 Torr. Next adimethyldichlorosilane (DDMS) precursor was introduced into the processchamber until the total pressure was in the range of 2.5-3 Torr. Thereaction was carried out for 10-15 minutes, after which time the chamberwas pumped out and vented with nitrogen. It was concluded thatincreasing substrate temperature during coating over a range of 20° C.to 50° C., all other variables being equal, results in films that havedecreasing water contact angle. The main result of the temperatureexperiments is said to be that there is no need to heat the sample. In asecond article entitled: “Vapor Deposition of Amino-FunctionalizedSelf-Assembled Monolayers on Mems”, Reliability, Testing, andCharacterization of MEMS MOEMS II”, Rajeshuni Ramesham, Danelle M.Tanner, Editors, Proceedings of SPIE Vol. 4980 (2003), authors MatthewG. Hankins et al. describe microengine test devices coated with filmsmade from amino-functionalized silanes. The coatings were applied in avapor-deposited self-assembled monolayer system developed at SandiaNational Laboratories. The process variables used to deposit thecoatings are not discussed in the article.

U.S. Pat. No. 6,576,489 to Leung et al., issued Jun. 10, 2003 describesmethods of forming microstructure devices. The methods include the useof vapor-phase alkylsilane-containing molecules to form a coating over asubstrate surface. The alkylsilane-containing molecules are introducedinto a reaction chamber containing the substrate by bubbling ananhydrous, inert gas through a liquid source of thealkylsilane-containing molecules, to transport the molecules in thevapor phase into the reaction chamber. The formation of the coating iscarried out on a substrate surface at a temperature ranging betweenabout 15° C. and 100° C., at a pressure in the reaction chamber which issaid to be below atmospheric pressure, and yet sufficiently high for asuitable amount of alkylsilane-containing molecules to be present forexpeditious formation of the coating. The liquid source of alkylsilanemolecules may be heated to increase the vapor pressure of thealkylsilane-containing molecules.

While various methods useful in applying layers and coatings tosemiconductor devices and MEMS have been discussed above and there issome description of the kinds of apparatus which may be employed todeposit the coatings, the apparatus description is minimal. Thefollowing references deal more with apparatus. U.S. Patent ApplicationPublication No. U.S. 2001/0028924 A1 of Arthur Sherman, published Oct.11, 2001, pertains to a method of sequential chemical vapor depositionwhich is used to deposit layers of inorganic materials such as SiO_(x),Al₂O₃, TiO₂, Si₃N₄, SiO_(x)N_(y), and aluminum films doped with copperand silicon. U.S. Patent Application Publication No. U.S. 2002/0076507A1 of Chiang et al., published Jun. 20, 2002, describes an atomic layerdeposition (ALD) process based on the sequential supply of at least twoseparate reactants into a process chamber. A first reactant reacts(becomes adsorbed) with the surface of the substrate via chemisorption.The first reactant gas is removed from the process chamber, and a secondreactant gas reacts with the adsorbed reactant to form a monolayer ofthe desired film. The process is repeated to form a layer of a desiredthickness. To reduce the process time, there is no separate purge gasused to purge the first reactant gas from the chamber prior tointroducing the second gas, containing the second reactant. Instead, thepurge gas also includes the second reactant. Several valving systems forgas flow to provide various mixtures of gases are described in detail.

The background information above provides a number of methods forgeneration of coatings which have considerable commercial applicability.The apparatus described for producing layers or coatings for use inelectronic devices and/or micro-electromechanical systems devicesenables application of the layers or coatings, but does not providesufficient accuracy and repeatability in terms of the amount of thevaporous reactants provided to the substrate surface. As a result, theprecise composition of the layer or coating which is desired may not beavailable. At other times, because of the improper ratio of variousreactants relative to each other, or oversaturation by a precursor,reactants may polymerize and/or particulate agglomerations may be formedwhich act as surface contaminants. Further, the ability to reproduce thesame coating reliably, time after time, is diminished due to lack ofcontrol over the precise amount of reactants supplied to the coatingformation process. This decreases the product yield and affects thecommercial viability of a coating process. It would be highly desirableto have a more accurate and reliable method of supplying precisequantities of the reactants to the process chamber and to the substratesurface for coating formation.

SUMMARY OF THE INVENTION

We have developed an improved vapor-phase deposition method andapparatus for the application of layers and coatings on substrates. Themethod and apparatus are useful in the fabrication of electronicdevices, micro-electromechanical systems (MEMS), Bio-MEMS devices, andmicrofluidic devices. The coating formation method employs a batch-likeaddition and mixing of all of the reactants to be consumed in a coatingformation process. The coating formation process may be complete afterone step, or may include a number of individual steps, where differentor repetitive reactive processes are carried out in each individualstep. The apparatus used to carry out the method provides for theaddition of a precise amount of each of the reactants to be consumed ina single reaction step of the coating formation process. The apparatusmay provide for precise addition of quantities of different combinationsof reactants during a single step or when there are a number ofdifferent individual steps in the coating formation process. The preciseaddition of each of the reactants is based on a metering system wherethe amount of reactant added in an individual step is carefullycontrolled. In particular, the reactant in vapor form is metered into avapor reservoir with a predetermined set volume at a specifiedtemperature to a specified pressure to provide a highly accurate amountof reactant. The entire measured amounts(s) of each reactant is (are)transferred in batch fashion into the process chamber in which thecoating is formed. The order in which each reactant is added to thechamber for a given reaction step is selectable, and may depend on therelative reactivities of the reactants when there are more than onereactant, the need to have one reactant or the catalytic agent contactthe substrate surface first, or a balancing of these considerations.

In some instances, it may be necessary to carry out a series ofindividual vapor delivery steps to provide a complete coating, ratherthan carrying out one continuous reaction process. For example, all of aprecisely measured quantity of one reacting component may be addedinitially, followed by a series of precisely measured quantities of asecond reacting component. In each case all of the measured quantity isadded to the reaction chamber. This provides a precise, carefullymeasured quantity of reactant at a precise time for each reactant.

A computer driven process control system may be used to provide for aseries of additions of reactants to the process chamber in which thelayer or coating is being formed. This process control system typicallyalso controls other process variables, such as, (for example and not byway of limitation), process time, chamber pressure, temperatures of theprocess chamber and the substrate to which the coating is applied, aswell as temperatures of the vapor delivery lines and vapor reservoirsrelative to the temperatures of the precursors.

The apparatus for vapor deposition of coatings is particularly usefulfor deposition of coatings having a thickness ranging from about 5 Å toabout 1,000 Å, (and may be used for increased coating thicknesses),where at least one precursor used for formation of the coating exhibitsa vapor pressure below about 150 Torr at a temperature of 25° C. Theapparatus includes at least one precursor container in which at leastone precursor, in the form of a liquid or solid, is placed; at least oneprecursor vapor reservoir for holding vapor of the at least oneprecursor; at least one device which controls precursor vapor flow fromthe precursor container into the precursor vapor reservoir; a pressuresensor in communication with the precursor vapor reservoir; a processcontroller which receives data from the pressure sensor, compares thedata with a desired nominal vapor reservoir pressure, and sends a signalto a device which controls vapor flow from the precursor container intothe precursor vapor reservoir, to prevent further vapor flow into theprecursor vapor reservoir when the desired nominal pressure is reached;a device which controls precursor vapor flow into the precursor vaporreservoir upon receipt of a signal from the process controller; aprocess chamber for vapor deposition of the coating on a substratepresent in the process chamber; and a device which controls precursorvapor flow into the process chamber upon receipt of a signal from theprocess controller.

In some instances, the apparatus includes a device which applies heat tothe precursor while it is in the container, to produce a vaporous phaseof the precursor. Typically the apparatus includes at least one catalystcontainer, in which a catalyst, in the form of a liquid or a solid isplaced; and a catalyst vapor reservoir for holding vapor of thecatalyst, with the same basic elements facilitating transfer of catalystto the process chamber at those described with reference to a precursor.

A method of the invention provides for vapor-phase deposition ofcoatings, where at least one precursor used for formation of the coatingexhibits a vapor pressure below about 150 Torr at a temperature of 25°C. The method includes the steps of: a) providing a processing chamberin which the coating is vapor deposited; b) providing at least oneprecursor exhibiting a vapor pressure below about 150 Torr at atemperature of 25° C.; c) transferring vapor of the precursor to aprecursor vapor reservoir in which the precursor vapor accumulates; d)accumulating a nominal amount of the precursor vapor required for thevapor phase coating deposition; and e) adding the nominal amount of theprecursor vapor to the processing chamber in which the coating is beingdeposited. Typically at least one catalyst vapor is added to the processchamber in addition to the at least one precursor vapor, where therelative quantities of catalyst and precursor vapors are based on thephysical characteristics to be exhibited by the coating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional schematic of an apparatus 100 for vapordeposition of a coating, which apparatus employs the present inventionfor metering precise amounts of reactants to the coating formationprocess.

FIG. 2 shows a cross-sectional schematic view of an apparatus 200 of thekind shown in FIG. 1, where a number of substrates are processedsimultaneously.

FIG. 3 is a schematic illustrating a system 300 of the kind which couldbe used for production of a MEMS device where there are moving partswhich are formed by a release-etching process in system 304 and where,subsequent to the release-etch process, the MEMS device is transferredthrough a pressure controlled passageway 306 to a coatings applicationchamber 302 of the kind described with reference to FIG. 1.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

As a preface to the detailed description, it should be noted that, asused in this specification and the appended claims, the singular forms“a”, “an”, and “the” include plural referents, unless the contextclearly dictates otherwise.

We have developed an improved vapor-phase deposition method andapparatus for application of a thin (typically 5 Å to 1,000 Å thick, inand in some instances up to about 2,000 Å thick) film or coating to asemiconductor device substrate or a micro-electromechanical systemsdevice. The method and apparatus are employed when at least one of thereactants or a catalyst used in coating formation must be vaporizedprior to use, and where the amount of each reactant must be carefullycontrolled in terms of quantity available to react, in terms of timeavailable for reaction at a given process pressure, or a combination ofboth. The method is particularly useful in the deposition of thin filmsor coatings where the thickness of the film or coating ranges from about5 Å to about 500 Å, and provides excellent results for coatings having athickness in the range of about 300 Å.

As previously discussed herein, there are a multitude of applicationsfor such thin layers or coatings. For purposes of illustration,applicants will describe the method and apparatus of the presentinvention in terms of the tunable deposition of an organic monolayer;however, one skilled in the art of deposition of layers and coatingswill be able to use the concepts described for coatings which are notorganic, and/or not monolayers.

There is a particular interest at this time in anti-stiction layers andcoatings which are needed to enable reliable, long-term performance ofthe micro-electromechanical systems. Stiction (adhesion) of compliantmicromechanical parts is one of the key reliability issues that hasproven difficult to overcome. Conventionally, solution-basedantistiction monolayers have been used; however, more recently, due tocapillary stiction, particulation problems, and unsatisfactory quality,scalability, and reproducibility of the films produced by relativelylengthy wet processing, efforts are underway to develop vapor depositionmethods for the antistiction coatings. The vacuum processing and vaporphase deposition of antistiction coatings, including self-assembledmonolayers (SAMs) has provided higher quality films in general. Anintegrated vapor deposition process (including surface plasma treatmentin the same chamber) typically offers better control of surfacereactivity, while avoiding the potential for stiction betweenmicromechanical parts during application of the antistiction coating.

The embodiments described in the examples below are with reference tothe application of organic SAM coatings which are applied using vapordeposition techniques over the surface of a single crystal siliconsubstrate. The apparatus used for deposition of the coatings isavailable from Applied Microstructures, Inc. of San Jose, Calif. Thisapparatus is specifically designed to provide a high degree of controlin terms of quantity of reactants provided to the coating applicationprocessing chamber for each individual process step, and in terms of thetime and order at which these reactants are made available for thereaction.

The properties of the deposited films were evaluated using standardsurface analysis methods, cantilever-beam-array test structures, andperformance analysis of working MEMS devices.

I. An Apparatus for Vapor Deposition of Thin Coatings

FIG. 1 shows a cross-sectional schematic of an apparatus 100 for vapordeposition of thin coatings. The apparatus 100 includes a processchamber 102 in which thin (typically 5 Å to 1,000 Å thick) coatings arevapor deposited. A substrate 106 to be coated rests upon a substrateholder 104, typically within a recess 107 in the substrate holder 104.Depending on the chamber design, the substrate 106 may rest on thechamber bottom (not shown in this position in FIG. 1). Attached toprocess chamber 102 is a remote plasma source 110, connected via a valve108. Remote plasma source 110 may be used to provide a plasma which isused to clean and/or convert a substrate surface to a particularchemical state prior to application of a coating (which enables reactionof coating species and/or catalyst with the surface, thus improvingadhesion and/or formation of the coating); or may be used to providespecies helpful during formation of the coating (not shown) ormodifications of the coating after deposition. The plasma may begenerated using a microwave, DC, or inductive RF power source, orcombinations thereof. The process chamber 102 makes use of an exhaustport 112 for the removal of reaction byproducts and is opened forpumping/purging the chamber 102. A shut-off valve or a control valve 114is used to isolate the chamber or to control the amount of vacuumapplied to the exhaust port. The vacuum source is not shown in FIG. 1.

The apparatus 100 shown in FIG. 1 is illustrative of a vapor depositedcoating which employs two precursor materials and a catalyst. Oneskilled in the art will understand that one or more precursors and fromzero to multiple catalysts may be used during vapor deposition of acoating. A catalyst storage container 116 contains catalyst 154, whichmay be heated using heater 118 to provide a vapor, as necessary. It isunderstood that precursor and catalyst storage container walls, andtransfer lines into process chamber 102 will be heated as necessary tomaintain a precursor or catalyst in a vaporous state, minimizing oravoiding condensation. The same is true with respect to heating of theinterior surfaces of process chamber 102 and the surface of substrate106 to which the coating (not shown) is applied. A control valve 120 ispresent on transfer line 119 between catalyst storage container 116 andcatalyst vapor reservoir 122, where the catalyst vapor is permitted toaccumulate until a nominal, specified pressure is measured at pressureindicator 124. Control valve 120 is in a normally-closed position andreturns to that position once the specified pressure is reached incatalyst vapor reservoir 122. At the time the catalyst vapor in vaporreservoir 122 is to be released, valve 126 on transfer line 119 isopened to permit entrance of the catalyst present in vapor reservoir 122into process chamber 102 which is at a lower pressure. Control valves120 and 126 are controlled by a programmable process control system ofthe kind known in the art (which is not shown in FIG. 1).

A Precursor 1 storage container 128 contains coating reactant Precursor1, which may be heated using heater 130 to provide a vapor, asnecessary. As previously mentioned, Precursor 1 transfer line 129 andvapor reservoir 134 internal surfaces are heated as necessary tomaintain a Precursor 1 in a vaporous state, avoiding condensation. Acontrol valve 132 is present on transfer line 129 between Precursor 1storage container 128 and Precursor 1 vapor reservoir 134, where thePrecursor 1 vapor is permitted to accumulate until a nominal, specifiedpressure is measured at pressure indicator 136. Control valve 132 is ina normally-closed position and returns to that position once thespecified pressure is reached in Precursor 1 vapor reservoir 134. At thetime the Precursor 1 vapor in vapor reservoir 134 is to be released,valve 138 on transfer line 129 is opened to permit entrance of thePrecursor 1 vapor present in vapor reservoir 134 into process chamber102, which is at a lower pressure. Control valves 132 and 138 arecontrolled by a programmable process control system of the kind known inthe art (which is not shown in FIG. 1).

A Precursor 2 storage container 140 contains coating reactant Precursor2, which may be heated using heater 142 to provide a vapor, asnecessary. As previously mentioned, Precursor 2 transfer line 141 andvapor reservoir 146 internal surfaces are heated as necessary tomaintain Precursor 2 in a vaporous state, avoiding condensation. Acontrol valve 144 is present on transfer line 141 between Precursor 2storage container 146 and Precursor 2 vapor reservoir 146, where thePrecursor 2 vapor is permitted to accumulate until a nominal, specifiedpressure is measured at pressure indicator 148. Control valve 141 is ina normally-closed position and returns to that position once thespecified pressure is reached in Precursor 2 vapor reservoir 146. At thetime the Precursor 2 vapor in vapor reservoir 146 is to be released,valve 150 on transfer line 141 is opened to permit entrance of thePrecursor 2 vapor present in vapor reservoir 146 into process chamber102, which is at a lower pressure. Control valves 144 and 150 arecontrolled by a programmable process control system of the kind known inthe art (which is not shown in FIG. 1).

During formation of a coating (not shown) on a surface 105 of substrate106, at least one incremental addition of vapor equal to the vaporreservoir 122 of the catalyst 154, or the vapor reservoir 134 of thePrecursor 1, or the vapor reservoir 146 of Precursor 2 may be added toprocess chamber 102. The total amount of vapor added is controlled byboth the adjustable volume size of each of the expansion chambers(typically 50 cc up to 1,000 cc) and the number of vapor injections(doses) into the reaction chamber. Further, the process control system(not shown) may adjust the set pressure 124 for catalyst vapor reservoir122, or the set pressure 136 for Precursor 1 vapor reservoir 134, or theset pressure 148 for Precursor 2 vapor reservoir 146, to adjust theamount of the catalyst or reactant added to any particular step duringthe coating formation process. This ability to fix precise amounts ofcatalyst and coating reactant precursors dosed (charged) to the processchamber 102 at any time during the coating formation enables the preciseaddition of quantities of precursors and catalyst at precise timingintervals, providing not only accurate dosing of reactants andcatalysts, but repeatability in terms of time of addition.

This apparatus provides a very inexpensive, yet accurate method ofadding vapor phase precursor reactants and catalyst to the coatingformation process, despite the fact that many of the precursors andcatalysts are typically relatively non-volatile materials. In the past,flow controllers were used to control the addition of various reactants;however, these flow controllers may not be able to handle some of theprecursors used for vapor deposition of coatings, due to the low vaporpressure and chemical nature of the precursor materials. The rate atwhich vapor is generated from some of the precursors is generally tooslow to function with a flow controller in a manner which providesavailability of material in a timely manner for the vapor depositionprocess.

The present apparatus allows for accumulation of the vapor into anadequate quantity which can be charged (dosed) to the reaction. In theevent it is desired to make several doses during the progress of thecoating deposition, the apparatus can be programmed to do so, asdescribed above. Additionally, adding of the reactant vapors into thereaction chamber in controlled aliquots (as opposed to continuous flow)greatly reduces the amount of the reactants used and the cost of thecoating process.

FIG. 2 shows a cross-sectional schematic of an embodiment of a vapordeposition processing apparatus 200 which provides for the applicationof a thin coating to a plurality of substrates 206 simultaneously. Theapparatus 200 includes a process chamber 202 in which thin (5 Å to 1,000Å thick) coatings are vapor deposited. A plurality of substrates 206 tobe coated rest upon a substrate holder 204, which can be moved withinprocess chamber 202 using a device 209. Attached to process chamber 202is a remote plasma source 210, connected via a valve 208. Remote plasmasource 210 may be used to provide a plasma which is used to clean or toreact with (activate) a substrate surface prior to application of acoating or may be used to provide species helpful during or afterformation of the coating (not shown). As previously described, theplasma may be generated using a microwave, DC, or inductive RF powersource, or may be generated using a combination of power sources. Theprocess chamber 202 makes use of an exhaust port 212 for the removal ofreaction byproducts and for pumping/purging of the process chamber 202.A control valve 214 is used to control the speed of vacuum pumping andevacuation (vacuum generator not shown).

The apparatus 200 shown in FIG. 2 is illustrative of a vapor depositedcoating which employs two precursor materials and a catalyst. Oneskilled in the art will understand that one or more precursors and fromzero to multiple catalysts may be used during vapor deposition of acoating. Catalyst for use during the coating deposition process entersprocess chamber 202 from a catalyst vapor reservoir (not shown) throughline 219 through control valve 220. Precursor 1 for use during thecoating deposition process enters process chamber 202 from a Precursor 1vapor reservoir (not shown) through line 217 through control valve 218,and Precursor 2 enters process chamber 202 from a Precursor 2 vaporreservoir (not shown) through line 215 through control valve 216. Aspreviously mentioned transfer lines for the Catalyst, Precursor 1, andPrecursor 2 are heated as necessary to maintain these materials in avaporous state, avoiding condensation. The Catalyst, Precursor 1 andPrecursor 2 may be distributed within process chamber 202 through abaffling system 205 which typically contains separate distribution pathsfor the catalyst and each precursor used in the coating depositionprocess. The baffling system helps ensure even distribution of eachreaction component material throughout process chamber 202. Processchamber 202 typically uses a swing door or a load lock 226. Uponcompletion of the reaction, process byproducts exit process chamber 202through exhaust port 212, which is connected to a vacuum pump (notshown). The interior surfaces of process chamber 200 and other apparatussuch as baffling system 205 are typically heated to prevent condensationof the Catalyst, Precursor 1, and Precursor 2 upon these apparatussurfaces. The reaction pressure is typically determined by the amount ofreactants injected into chamber 202. The processing chamber pressure ismonitored by pressure sensing device 224, which is coordinated with thevapor delivery system previously described through a computerizedcontrol system (not shown). A flow control valve 214 is used to removevapor and byproducts in general from the interior of process chamber202. The operation of flow control valve 214 may be coordinated, throughthe computerized control system, to function in combination with thepressure sensing device, to maintain the desired pressure duringpumping/purging steps.

FIG. 3 shows a cross-sectional schematic of a MEMS processing system 300which employs a release-etch processing chamber 310 (of the type used toproduce moveable elements of a mechanical nature in a MEMS device) and avapor deposition coating application system 312 of the kind previouslydescribed with reference to FIGS. 1 and 2. The release-etch processchamber 310 includes apparatus for reagent entry 324 (shown as a singleline for convenience, but which may be a plurality of lines); a pressuresensing and monitoring device 326; an exhaust port 334, with flowcontrol valve 332; a recirculation loop 331 with pump 330 is optional,but can be used to provide important processing advantages. The vapordeposition coating apparatus process chamber 308 includes apparatus forreagent (catalyst and precursor) entry 312 (shown as a single line forconvenience, but which is a plurality of lines as previously discussed);a pressure sensing and monitoring device 314; and an exhaust port 322,with a control valve 320. The release-etch process chamber 310 and vapordeposition coating process chamber 308 are joined to each other throughan isolation valving system 306.

II. Exemplary Methods of the Invention:

As discussed with respect to the apparatus, there have been problems inproviding accurately measured quantities of reactants on a repeatablebasis to a vapor deposition coating system. This is because many of theprecursor materials for coating formation have a low vapor pressure orare not compatible with mass flow controllers. In addition, for many ofthe vapor deposition coatings, water acts as a catalyst to the coatingformation, and the amount of water present in the coating depositionchamber is not precisely controlled.

When the surfaces of features to be coated are in the nanometer sizerange, it is critical that the coating deposition be carefullycontrolled to provide the desired thickness of coating (typically about5 Å to 1,000 Å, and in some instances up to 2,000 Å) over the entiresurface area, and that there be no formation of particulate oragglomerations within the depositing coating. In order to meet thesecritical requirements for thin vapor deposited coatings, it is necessaryto provide accurately measured quantities of reactants and catalysts andto control the time period over which these accurately measuredquantities are delivered to the surface of the substrate or thedeposition chamber. Delivery to the surface of the substrate depends oninterior design of the processing chamber, and there are techniqueswhich are well known in the art of chemical vapor deposition which applyto delivery of reagents to the substrate surface. The present methodaddresses the problem of providing accurately measured quantities ofreactants and catalysts which are delivered in the proper order and atthe proper time to the coating deposition chamber.

By way of example and not by way of limitation, the provision ofaccurate quantities of reactants and catalysts will be illustrated withrespect to monolayer coatings of chloro-silanes and alkyl-silanes whichare used in many applications such as MEMS, BioMEMS, and micro-fluidics.Organic precursor materials such as (and not by way of limitation)silanes, chlorosilanes, fluorosilanes, methoxy silanes, alkyl silanes,and amino silanes are useful in general. Some of the particularprecursors used to produce coatings are, by way of example and not byway of limitation, perfluorodecyltrichlorosilanes (FDTS),undecenyltrichlorosilanes (UTS), vinyl-trichlorosilanes (VTS),decyltrichlorosilanes (DTS), octadecyltrichlorosilanes (OTS),dimethyldichlorosilanes (DDMS), dodecenyltricholrosilanes (DDTS),fluoro-tetrahydrooctyldimethylchlorosilanes (FOTS),perfluorooctyldimethylchlorosilanes, aminopropylmethoxysilanes (APTMS),fluoropropylmethyldichlorosilanes, andperfluorodecyldimethylchlorosilanes. The OTS, DTS, UTS, VTS, DDTS, FOTS,and FDTS are all trichloro silane precursors. The other end of theprecursor chain is a saturated hydrocarbon with respect to OTS, DTS, andUTS; contains a vinyl functional group, with respect to VTS and DDTS;and contains fluorine atoms with respect to FDTS (which also hasfluorine atoms along the majority of the chain length). Other usefulprecursors include 3-aminopropyltrimethoxysilane (APTMS), which providesamino functionality, and 3-glycidoxypropyltrimethoxysilane (GPTMS). Oneskilled in the art of organic chemistry can see that the vapor depositedcoatings from these precursors can be tailored to provide particularfunctional characteristics for a coated surface. The surface to becoated may be silicon, glass, organic (plastic) or metal, for example.

Most of the silane-based precursors, such as commonly used di- andtri-chlorosilanes, for example and not by way of limitation, tend tocreate agglomerates on the surface of the substrate during the coatingformation. These agglomerates can cause structure malfunctioning orstiction. Such agglomerations are produced by partial hydrolysis andpolycondensation of the polychlorosilanes. This agglomeration can beprevented by precise metering of moisture in the process ambient whichis a source of the hydrolysis, and by carefully controlled metering ofthe availability of the chlorosilane precursors to the coating formationprocess.

Those working in the MEMS field have recognized the advantages of vapordeposited coatings over coatings applied using liquid-based immersion,spray-on and spin-on techniques. Some of those advantages include:elimination of stiction induced by capillary forces; control of thecoating environment (particularly the amount of moisture present);uniform coating properties on micron and nanometer size patterns such asmicrochannels and pores; solvent free process with no contamination;and, a faster process which is compatible with MEMS clean roomprocessing protocols, for example.

In a vapor deposition process which employs one precursor and acatalyst, a DDTS precursor may be used in combination with a watercatalyst, for example. In a vapor deposition process which employs twoprecursors and a catalyst, a DDTS precursor, a UTS precursor, and awater catalyst may be used in combination, for example and not by way oflimitation. The relative quantities of the DDTS and UTS precursors canbe adjusted to provide different overall functional properties for thecoated surface. However, the ability to control the coated surfaceproperties and to reliably reproduce the properties depends on theability to control the relative quantities of the DDTS and UTSprecursors supplied to the coating formation process. This abilitydepends on provision of accurately controlled quantities of the kindwhich are possible when the present method of invention is used.

When the precursors used to form the initial vapor deposited coatinghave potentially reactive functional groups on the exposed surface ofthe coating, there functional groups can be further reacted with otherchemical compounds to modify the functionality of the surface of thecoating.

In addition to organo-silanes, poly(ethylene glycol) (PEG) is usedseparately or in combination with other film-forming compounds such asthe silanes to provide biotechnology functional surfaces. One portion ofthe coated surface may be coated with the reaction product of anorgano-silane, while another is coated with a PEG reaction product. Inthe alternative, the organo-silane may include a functional group on thedistal end of the polymer chain, away from the substrate surface, whichfunctional group can be reacted with a PEG reactant, to place a PEGfunctional group at the distal end of the polymer chain, affectingcoating surface functionality. For example, PEG films are known toreduce protein adsorption in micro-fluidic applications. PEG 3 filmsinclude 6 carbons, while PEG 2 films include 4 carbons. The length ofthe polymer chain can also be adjusted to provide the desired filmproperties.

The present method for vapor deposition of coatings provides a number ofadvantages. Typically a remote plasma source is used to generate acleaning plasma (typically oxygen-containing) which can be used toremove contaminants from the substrate surface. When the substrate issilicon, the cleaning process is useful in the formation of —OHfunctional groups which serve as binding sites for a number of coatingprecursors such as the trichloro silanes. Precise control of the amountof precursors is ensured through the direct measurement of the vaporpressure of the precursor at a given temperature in a known volume.Process control is provided by varying the partial pressure and theamount of the precursors employed in the vapor phase reaction.

III. General Parameter Descriptions for Vapor Deposition of a MolecularCoating:

Surfaces to be coated are typically pretreated in the same chamber. Toobtain bonding of a chloro-functional group to a substrate surface, itis necessary to create OH-terminated sites on the surface. This can bedone in the deposition chamber by treating a silicon surface with anoxygen plasma in the presence of moisture. The plasma may be producedusing a remote power source of the kind previously described. Thepressure in the processing chamber during exposure of a substrate to theoxygen plasma typically ranges from about 0.2 Torr to about 2 Torr, moretypically from about 0.5 Torr to about 1 Torr. For a process chamberhaving a volume of about 2 liters, the plasma source gas oxygen flowrate ranges from about 50 sccm to about 300 sccm, more typically fromabout 100 sccm to 200 sccm. The substrate processing time is typicallyabout 1 minute to about 10 minutes, and more typically from about 1minute to about 5 minutes.

The coating deposition is typically carried out in the depositionchamber at a pressure ranging from about 100 mTorr to about 10 Torr,more typically at a pressure ranging from about 0.5 Torr to about 5Torr, and most typically at a pressure ranging from about 0.1 Torr toabout 3 Torr. The deposition temperature of the substrate depends on theparticular coating precursors and on the substrate material. For asilicon substrate, where the coating precursor is FOTS or DDMS, used incombination with a water catalyst, the substrate temperature istypically in the range of about 20° C. to about 60° C. To maintain thesecoating precursors in a vaporous state prior to reaction, the interiorsurfaces of the coating deposition process chamber are typicallymaintained at a temperature ranging from about 30° C. to about 60° C.The time period required to produce a continuous monolayer coating overthe entire surface of the silicon substrate using these coatingprecursors and the specified reaction temperature ranges from about 1minute to about several hours, depending on precursor chemistry andsubstrate material, typically the reaction time period is in the rangeof 5 minutes to 30 minutes, where the coating precursor is FOTS or DDMS.

For deposition of an antistiction MEMS coating from chlorosilaneprecursors, the following recipe and process conditions were used. Ineach case, a single precursor, selected from the group consisting ofdimethyldichlorosilane (DDMS),tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (FOTS), andheptadecafluoro-1,1,2,2-tetrahydrodecyltrichlorosilane (FDTS), wasvaporized and used in combination with water vapor as a catalyst. Ineach instance, the precursor and the water were degassed under vacuum toremove dissolved gases prior to introduction into the system. Theconditions for degassing vary, depending on the precursor and catalyst,but one skilled in the art can easily determine proper degassingconditions.

With reference to FIG. 1, the degassed water was placed in catalyststorage container 116 and was heated to a temperature of about 30° C. toproduce a vapor which was passed through transfer line 119 to accumulatein vapor reservoir 122, which had a volume of 300 cc, and which was heldat a pressure of 16 Torr. A DDMS precursor was placed in Precursor 1storage container 128 and was heated to a temperature of 30° C. toproduce a vapor which was passed through transfer line 129 to accumulatein vapor reservoir 134, which had a volume of 50 cc, and which was heldat a pressure of 50 Torr. There was no precursor in Precursor 2 storagecontainer 140.

A silicon substrate 106, having a surface 105 was manually loaded ontothe substrate holder 104. The process chamber 102, having a volume ofabout 2 liters, was pumped down to about 20 mTorr and purged withnitrogen gas prior to and after the coating reaction, which consisted ofoxygen plasma treatment followed by coating deposition. The processchamber 102 was vented to atmosphere. The process chamber 102 was thenpurged using nitrogen (filled with nitrogen to 10 Torr/pumped to 0.7Torr, five times). The surface 105 was treated with a remotely generatedoxygen plasma from plasma source 110 in the manner described above.Oxygen was directed into a plasma generation source 110 through a massflow controller (not shown). The oxygen flow rate for plasma generation,based on the desired plasma residence time for process chamber 102, wasabout 200 sccm. The pressure in process chamber 102 was about 0.6 Torr.The surface 105 of silicon substrate 106 was treated with the oxygenplasma at a pressure of about 0.6 Torr for a time period of about 5minutes. The plasma treatment was discontinued, and the process chamber102 was pumped down to the base pressure of about 30 mTorr.

The water vapor reservoir 122 was charged with water vapor to a pressureof 16 Torr, as described above. The valve 126 between water vaporreservoir 122 and process chamber 102 was opened until both pressuresequalized (a time period of about 5 seconds) to about 0.8 Torr. Thewater vapor reservoir 122 was charged with vapor to 16 Torr a secondtime, and this volume of vapor was also dumped into the process chamber,bringing the total water vapor pressure in process chamber 102 to about1.6 Torr. The DDMS vapor reservoir 134 had been charged with theprecursor vapor to 50 Torr, as described above, and the DDMS vapor wasadded immediately after completion of the water vapor addition. Thevalve 138 between the DDMS vapor reservoir 134 and process chamber 102was opened until both pressures were equalized (a time period of about 5seconds) to about 4 Torr. The water and DDMS vapors were maintained inprocess chamber 102 for a time period of 15 minutes. The process chamberwas then pumped back to the base pressure of about 30 mTorr.

The process chamber 102 was then purged (filled with nitrogen to 10Torr/pumped to 0.7 Torr) five times. The process chamber was then ventedto atmosphere, and the silicon substrate 106 was manually removed fromthe process chamber.

The resulting coated surface is typically very hydrophobic, as measuredby water contact angle, which is typically about 103° for DDMS films.The surface was particularly smooth, having an RMS of 0.2 nm, with novisible particulation or defects. The measured work of adhesion wasreduced up to 3,000 times depending on the specific process/chemistry.Under the conditions provided above, the measured work of adhesion wasreduced to about 30 μJ⁻². The properties of the vapor deposited filmsare equivalent to or better than those reported for liquid-phasedeposited films; In addition, use of vapor deposition prevents thestiction which frequently occurs during wet processing of the substrate.

The above described exemplary embodiments are not intended to limit thescope of the present invention, as one skilled in the art can, in viewof the present disclosure expand such embodiments to correspond with thesubject matter of the invention claimed below.

1-10. (canceled)
 11. A method for vapor-phase deposition of coatings,where at least one precursor used for formation of said coating exhibitsa vapor pressure below about 150 Torr at a temperature of 25° C., themethod comprising: a) providing a processing chamber in which saidcoating is vapor deposited; b) providing at least one precursorexhibiting a vapor pressure below about 150 Torr at a temperature of 25°C.; c) transferring vapor of said precursor to a precursor vaporreservoir in which said precursor vapor accumulates; d) accumulating anominal amount of said precursor vapor required for said vapor phasecoating deposition; and e) adding said nominal amount of said precursorvapor to said processing chamber in which said coating is beingdeposited.
 12. A method in accordance with claim 11, wherein a pluralityof precursors are used, and wherein a plurality of precursors areaccumulated in a plurality of precursor vapor reservoirs.
 13. A methodin accordance with claim 12, wherein at least two of said precursorvapors are added to said processing chamber essentially simultaneously.14. A method in accordance with claim 12, wherein at least two of saidprecursor vapors are added to said processing chamber in sequence.
 15. Amethod in accordance with claim 11, wherein at least one catalyst vaporis added to said processing chamber to facilitate vapor deposition ofsaid coating.
 16. A method in accordance with claim 15, wherein saidcatalyst vapor is accumulated in a vapor reservoir prior to transfer tosaid processing chamber.
 17. A method in accordance with claim 16,wherein said catalyst vapor is added to said processing chamberessentially simultaneously with at least one of said at least oneprecursor vapors.
 18. A method in accordance with claim 16, wherein saidcatalyst vapor is added to said processing chamber in sequence with atleast one of said precursor vapors.
 19. A method in accordance withclaim 18, wherein said catalyst vapor is added to said processingchamber prior to the addition of a precursor vapor to said processingchamber.
 20. A method in accordance with claim 11, wherein at least oneof said precursor vapors is added to said process chamber from saidvapor reservoir more than once, by repeating steps c), d), and e).
 21. Amethod in accordance with claim 15, wherein at least one of said atleast one catalyst vapor is added to said process chamber from saidvapor reservoir more than once, by repeated filling of a nominal vaporreservoir volume, followed by repeated adding of said vapor catalyst tosaid process chamber from said vapor reservoir.
 22. A method inaccordance with claim 11, wherein a plurality of precursor vapors areadded to said process chamber and wherein said precursor vapors areadded in relative quantities required to produce coating physicalcharacteristics.
 23. A method in accordance with claim 15, wherein atleast one catalyst vapor is added to said process chamber in a quantityrelative to said at least one precursor vapor to produce a coatinghaving specific physical characteristics.
 24. A method in accordancewith claim 23, wherein a volumetric ratio of a precursor to a catalystranges from about 1:6 to about 6:1.
 25. A method in accordance withclaim 24, wherein said volumetric ratio ranges from about 1:3 to about3:1.
 26. A method in accordance with claim 12, wherein at least one ofsaid precursor vapors is added to said process chamber from said vaporreservoir more than once, by repeating steps c), d), and e).
 27. Amethod in accordance with claim 16, wherein at least one of said atleast one catalyst vapor is added to said process chamber from saidvapor reservoir more than once, by repeated filling of a nominal vaporreservoir volume, followed by repeated adding of said vapor catalyst tosaid process chamber from said vapor reservoir.
 28. A method inaccordance with claim 12, wherein a plurality of precursor vapors areadded to said process chamber and wherein said precursor vapors areadded in relative quantities required to produce coating physicalcharacteristics.
 29. A method in accordance with claim 16, wherein atleast one catalyst vapor is added to said process chamber in a quantityrelative to said at least one precursor vapor to produce a coatinghaving specific physical characteristics.
 30. A method in accordancewith claim 29, wherein a volumetric ratio of a precursor to a catalystranges from about 1:6 to about 6:1.
 31. A method in accordance withclaim 30, wherein said volumetric ratio ranges from about 1:3 to about3:1.